Planting a tree to cool the earth has spread like fire, an initiative inspired by Nobel Peace Prize Winner Wangari Maathai. Since its launch in 2006 by the United Nations Environment Programme (UNEP), the Billion Tree Campaign has mobilized tree-planting efforts worldwide, with children, communities, governments and CEOs getting their hands dirty in the act.

To date, more than two billion trees have been planted in 160 countries. This campaign is just one of the three UNEP projects that has won an award. The UN21 Awards are given out each year by the United Nations' Secretary-General to recognize 15 outstanding initiatives across the organization.

China gets greener in Gangchen, Shigatse district.The other two winning UNEP projects are the Indian Solar Loan Programme and the Iraqi Marshlands projects. "The three projects, which join 12 others from across the entire UN system, reflect the new or perhaps newly-understood challenges facing the UN in the 21st century. Namely climate change and the key role of the environment towards peace, stability and development," said UNEP Executive Director Achim Steiner.

In May, UNEP announced its new goal of planting seven billion trees by the Copenhagen climate change meeting in 2009.

You can be part of this green cover revolution just where you live or work. Here’s how:

Preparing to Plant a TreeThe ideal time to plant a tree in the tropics and subtropics is during the rainy season. In temperate zones, choose the dormant season, after leaf drop or before bud break. An exception would be trees that have been well cared for in a nursery - these can be planted throughout the growing season.

Seeds can be sown in seed beds or seedling containers (preferably biodegradable) prepared with a mixture of sand, compost and soil. The plants will need watering before and after germination. Reduce the frequency of watering as the seedlings grow. Shade the seedlings and gradually reduce the shade as they grow.

Collect seeds from an area that enjoys similar climatic conditions to where the trees will be planted, and do so from a number of healthy mature trees.

All Prepared? Let’s Get DirtyTusco Trafo staff plant 5000 mangrove trees in Thailand.1. Dig a hole at least twice the width of the root ball to allow the roots to spread out. Remove the tree from its container, carefully cut off broken roots, and slightly loosen the root ball.2. Place the tree in the planting hole. Always lift the tree by the root ball and never by the trunk. Spread periphery roots outwards. Avoid planting too deep. Make sure that the soil line of the young tree is higher than the surface of the surrounding hole.3. Shovel some soil into the planting hole. Check the planting depth and adjust if needed. Confirm that the tree is straight. Fill the hole gently but firmly. Pat the soil around the base of the root ball.4. Water the seedling thoroughly with a slow stream of water to settle the soil. Do not stake the tree. The sooner the tree can stand alone, the sooner it will become strong. It is not recommended to apply fertilizer at the time of planting.5. Continue caring by eradicating pests and diseases. Remove weeds as they will compete with tree roots for moisture and nutrients. 6. Space trees well to avoid competition for air and soil nutrients, and to encourage the growth of branches. Watch out for yellowing of leaves. Always maintain good air circulation in the tree by pruning to avoid pests and other diseases.Contact an arborist or a nearby environmental organization for advice on caring for your tree.